-is the one that encodes the variable `x`, the line that begins `(Leaf
-(Num (fun x -> ...`. The fifth line you need to modify is the one
-that replaces "4" with "y". When you have these lines modified,
+is the one that encodes the variable `n`, the line that begins `(Leaf
+(Num (fun n -> ...`. The fifth line you need to modify is the one
+that replaces "4" with "m". When you have these lines modified,